Organophosphorus compounds and methods for the preparation thereof



ABSTRACT on THE DISCLOSURE 3,5-di-alkyl (andcycloalkyl)-4-hydroxyphenylphosphonous and phosphinous) acids are newcompounds, useful to stabilize organic materials, such as lubricants,hydrocarbons, fuels, and plastics against oxidation and the effects oflight and heat. Methods for manufacture of such compounds by reaction of2,6-dialkyl (and cyclohexyl) phenols with a phosphorus trihalide in thepresence of a tertiary amine and subsequent hydrolysis of the productmade are also described.

This application is a continuation-in-part of our copending applicationSer. No. 220,901, filed Aug. 31, 1962, and now abandoned.

This invention relates to organophosphorus compounds. More particularly,it relates to hydroxyp'henylphosphonous and hydroxyphenylphosphinousacids and methods for the preparation thereof.

Various types of aromatic phosphonous acids and hisaromatic phosphinousacids are known to the art. Most of these, however, require the use ofaluminum chloride as a catalyst in their preparation. This catalyst,apart from contributing to the cost of the synthesis, complicates therecovery of the product. The complications which are involved inrecovery of theproduct from the aluminum chloridecatalyst are set forthon pages 44 and 128 of Kosolapoffs Organo-Phosphorus Compounds, SecondEdition (1958), published by John Wiley & Sons, Inc.

Therefore, an object of this invention is to provide a method ofpreparing organo-phosphonous acids and organo-phosphinous acids withouta catalyst.

Another object of this invention is to provide novelhydroxyphenylphosphonous acids.

A further object of this invention is to provide novel bis(hydroxyphenyl phosphinous acids.

Still further objects and the scope of applicability of the presentinvention will be come apparent from the detailed description givenhereinafter; it should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

It has been found that novel hydroxyphenylphosphonous acids and novelbis(hydroxyphenyl)phosphinous acids can be prepared by reacting asubstituted phenol with a phosphorus trihalide, in the presence of ahalogen acid acceptor, such as an amine, preferably a tertiary amine.

The temperature and pressure at which the reaction of this invention iscarried out are dictated largely by convenience and depend upon theboiling point of phosphorus trihalide. Thus, the boiling point ofphosphorus trichloride is 7-6 degrees centigrade and to react thiscomposition much above 76 degrees centigrade would require pressureequipment. However, subatmospheric and superatmospheric pressures can beused if desired. The reaction is preferably carried out at a temperatureof from about ten degrees centigrade to about 25 degrees centigradewithout the presence of a catalyst.

The reaction is completed when, in the presence of a tertiary amine, aprecipitate no longer continues to form. Another way to test forcompletion of the reaction is to test for the halide and determine thatthe evolution of halogen acid is complete. The halogen halide by-productof the reaction may then be separated by evaporation in instances wherea tertiary amine is not utilized. The other remaining volatileby-products are removed by distillation at reduced pressure, leaving aresidue. The desired product is then removed from the residue byhydrolysis and crystallization of the resulting solids.

It has been further found that both products of this invention may beobtained; i.e., a hydroxyphenylphosphonous acid and a his(hydroxyphenyl)phosphinous acid, from the same reaction mixture. Therelative amounts of each, however, may be varied by varying themolecular ratio of the reactants. For example, if ahydroxyphenylphosphonous acid is the desired product, then one mole ofsubstituted phenol may be reacted with an excess of the phosphorustrihalide, and if the bis(hydroxyphenyl)phosphinous acid is desired, onemole of phosphorus halide can be reacted with an excess of thesubstiuted phenol.

The hydroxyphenylphosphonous acids may be separated from thebis(hydroxyphenyl)phosphinous acids by means of their dilference inacidity. The hydroxyphenylphosphonous acid, being a strong monobasicacid, readily forms water-soluble sodium salts whereas thebis(hydroxyphenyl)phosphinous acid, being an extremely weak acid, showslittle acidity, except in a non-aqueous medium. Thus, in consequence, itdoes not dissolve appreciably in dilute aqueous caustic and may beseparated from the hydroxyphenylphosphonous acid. The latter forms asoluble sodium salt and the former remains as an insoluble residue inthe aqueous caustic.

Although phosphorus trichloride is preferred for the purpose ofillustration, it is to be understood that phosphorus triiodide,tribromide, and trifluoride may also be used in suitable reactions.Metal halides and other halides may also be used in the practice of thisinvention, such as the halides o-f antimony, arsenic, silicon and boron.

The substituted phenols which may be used in this invention have thegeneral formula:

wherein Y and Y are organic radicals containing at least one carbonatom.

For purposes of this invention 2,6-t-butyl phenol is reacted withphosphorus trichloride. However, other 2,6-dilower alkyl phenols may beused, such as 2,6-dimethyl phenol, 2,6-diethyl phenol, 2,6-diisopropylphenol, Z-ethyl- 6-secondary butyl phenol, dicyclohexyl phenol, andlower alkyl substituted cyclohexyl phenol. Usually the alkyl groups Yand Y, which may be the same or different, are lower alkyl, of 1 to 10carbon atoms each and preferably are of 1 to 6 carbon atoms each.Tertiary alkyls, such as t-butyl, are also preferred. The newhydroxyphenylphosphonous and bis (hydroxyphenyl) phosphinous 3 acidsformed by the reaction of this invention have the general formula:

wherein Y and Y are organic radicals containing at least one carbon atomand n and z are integers from 1 to 2, z being 2 when n is 1 and 1 when nis 2.

Some examples of the products formed by the process of this inventionare 3,5-dimethyl-4-hydroxyphenylphosphonous acid;bis(3,5-dimethyl-4-hydroxyphenyl)phosphinous acid;3,5-diethyl-4-hydroxyphenylphosphonous acid;bis(3,5-diethyl-4-hydroxyphenyl) phosphinous acid;3,5-diisopropyl-4-hydroxyphenylphosphonous acid; bis(3,5-diisopropyl4-hydroxyphenyl)phosphinous acid; 3- ethyl-S-secondarybutyl-4-phenylphosphonous acid; bis(3- ethyl 5 secondarybutyl-4-hydroxyphenyl)phosphinous acid;3,5-dicyclohexyl-4-hydroxyphenylphosphonous acid; and bis(3,5dicyclohexyl-4-hydroxyphenyl)phosphinous acid.

The products of this invention, i.e., the hydroxyphenyl phosphonous andbishydroxyphenylphosphinous acids are useful as inhibitors, stabilizers,antioxidants, lubricant additives and as biologically active materials.Thus, they may be used to stabilize hydrocarbon materials, such aslubricants and fuels and inhibit oxidation thereof, even when employedonly to the extent of from .01 percent to 1 percent of the compositions.Preferably, from 0.05 to 0.5 percent of the products of this inventionare employed. They are similarly useful as stabilizers in plastics, suchas polyvinyl chloride, and in monomers for use in plastics, such asstyrene.

The following examples illustrate ways in which the invention has beenpracticed and the advantages accruing therefrom.

Example 1.-Preparation of 3,5-di-t-buty1-4- hydroxyphenylphosphonousacid A mixture of 413 grams of 2,6-di-t-butylphenol and 273 grams oftriethylamine was added dropwise to 1005 grams of PC1 in a vessel fromwhich moisture was excluded. Addition time was 2% hours. The temperaturewas maintained at to 20 degrees centigrade. After removal of the solidamine hydrochloride, unreacted reagents and byproducts were removed bydistillation at 1 mm. of mercury absolute pressure. The residue,amounting to 269 grams, was then ground up. A 100-gram portion of it wassuspended in 1 liter of water containing 40 grams of NaOH. This wasboiled for three hours and steam volatile material was distilled off.Upon cooling, a crystalline material separated. This was filtered off,washed with ether and dried; 82 grams were obtained. It was thenrecrystallized twice from water. The free acid was obtained byacidification with dilute HCl. After crystallization from a methanolwater mixture, it melted at 145 to 146 degrees centrigrade, and had thefollowing analysis:

Calculated for C H O P: C, 62.0%; H, 8.5%; P, 11.4%. Found: C, 62.3%; H,8.7%; P, 11.5%.

The material is a strong monobasic acid. The presence of the phenolic OHgroup was proven by a non-aqueous titration and by infrared spectra.Thus, it was established to be 3,S-di-t-butyl-4-hydroxyphenylphosphonous acid.

Example 2.Preparation of bis(3,5-di-t-butyl-4- hydroxyphenyl)phosphinous acid A mixture of 412 grams of 2,6-di-t-butylphenol and 267grams of triethylamine was added dropwise to 1012 grams of PCl over a 2%hour period at 22 to 25 degrees centigrade. The reaction mixture wasprotected from moisture. The solid amine hydrochloride was filtered offand the unreacted reagents and the 2,6-di-t-butyl-phenylphosphorodichloridite were then distilled off.

The residue, which weighed 230 grams, was ground up and added to 1.1liters of 10 percent aqueous sodium hydroxide. This mixture was boiledfor two and one-half hours. Steam volatile material was distilled off.The portion of residue which was not completely soluble in the hot basicsolution was filtered off, washed with acetone and dried; 43.5 gramswere obtained. After purification by crystallizing from benzene, itmelted at 207 to 208 degrees centrigrade, and had the followinganalysis:

Calculated for C H O P: C, 73.3%; H, 9.37%; P, 6.8%. Found: C, 73.8%; H,9.6%; P, 7.0%.

The compound reacts neutral in water. The presence of the phenolic OHgroups was proven by a non-aqueous titration and by its infraredspectrum. Thus, it was established as beingbis(3,5-di-t-butyl-4-hydroxyphenyl)phosphinous acid.

Example 3.-Antioxidant effects The compounds which were made in Examples1 and 2 were tested as peroxidation inhibitors and as stabilizers. As isshown by the following table, triisopropyl benzene was tested forhydroperoxide production after 48 hours in air at degrees centigrade,without any additive; with 0.1 percent of a known antioxidant(2,6-di-t-butylphenol); and with 0.1 percent of the compounds ofExamples 1 and 2.

TABLE Percent hydroperoxide present after 48 hours in air at 100 degreesCentigrade The results of this test prove that the compounds of thisinvention are useful antioxidants when tested against a typical aromaticcompound found in normally peroxidizable hydrocarbon motor fuels.

Example 4.-Stabilizing effects The compounds of this invention were alsotested for their stabilizing utility. Styrene monomer, when exposed todirect sunlight for 20 hours, solidifies. If unexposed to sunlight, thestyrene monomer remains liquid. In the presence of 0.05 percent of3,5-di-t-butyl-4-hydroxyphenyl phosphonous acid, even after beingexposed to sunlight for 20 hours, the styrene monomer is no more viscousthan unexposed material.

When the present phosphonous and phosphinous acids are employed as heatstabilizers in polyvinyl chloride, they are also effective at 0.25 partconcentration in 50 parts of polyvinyl chloride, by weight, 22 partsdioctyl phthalate and 4 parts of barium cadmium laurate. In ultraviolentradiation exposure tests, after 123 hours exposure, polyvinyl chloridecontaining such a very small proportion ofbis(3,5-di-t-butyl-4-hydroxyphenyl) phosphinous acid, only turned lightyellow, but a control, without the phosphinous acid, became gray.

In addition to their utility for peroxidation inhibition of organiccompounds, especially unsaturated hydrocarbons, and their stabilizingeffect on unsaturated compounds such as organic monomers and plastics,the new phosphonous and phosphinous acids are also useful chemicalintermediates for the syntheses of other substances. Thus, when oxidizedin acid medium, both 3,5-di-t-buty1- 4-hydroxyphenyl phosphonous acidand the corresponding bis-phosphinous acid yield the related phosphonicacids, while in alkaline medium the phosphonous acid yields a highlycolored substance, 3,3,5,5-tetra-t-butyl 5 diphenyl quinone. Similarresults are obtained with the other alkyl-substituted phosphonous andphosphinous acids of this invention.

What is claimed is: 1. A composition having the general formula: 5

L 011 ll wherein Y and Y are organic radicals selected from the groupconsisting of lower alkyl and cyclohexyl, and n and z are from 1 to 2, 2being 2 when n is 1 and 1 when n is 2.

2. A composition according to claim 1 wherein Y and Y are tertiary alkylgroups. 0

3. A compound according to claim 2 wherein n is 2 and Y and Y aretertiary butyl.

4. A compound according to claim 2 wherein n is 1 and Y and Y aretertiary butyl.

5. A process for having the formula:

preparing an organophosphorus acid 1 1 L if).

wherein Y and Y are organic radicals selected from the group consistingof lower alkyl and cyclohexyl, and n and z are from 1 to 2, 2 being 2when n is 1 and 1 when n is 2, comprising reacting a phenol having theformula:

45 wherein Y and Y are as described above, with a phosphorus trihalidein .the presence of a tertiary amine, distilling off the by-productformed to recover a residue, hydrolyzing said residue, and thereafterseparating the desired product.

6. A process in accordance with claim 5 wherein Y and Y are tertiarybutyl groups and the reaction of the phenol is with phosphorustrichloride under anhydrous conditions.

are selected from the group consisting cyclohexyl, n and z are integersfrom when n is 1 and 1 when n is 2, comphenol having the formula:

wherein Y and Y of lower alkyl and 1 to 2, z being 2 prising reacting awherein Y and Y are as described above, with a phosphorus trihalide inthe presence of a tertiary amine, separating the reaction product fromthe reaction mixture, and acidifying such reaction product to form thedesired organo-phosphorus acid.

References Cited UNITED STATES PATENTS 2,683,168 7/1954 Jensen et a1.260-543 3,183,264 5/1965 Rochlitz et a1 260543 3,210,418 10/1965Pianfetti 260-543 OTHER REFERENCES Kosolapofi: OrganophosphorusCompounds (1950), pp. 182, 183, 189.

Van Wazer: Phosphorus and Its Compounds, vol. 1 (1958), pp. 370, 373.

BERNARD HELFIN, Primary Examiner. J. E. EVANS, Assistant Examiner.

